A method of this kind is known from the marketplace. In the method, fuel is injected into an intake channel via an injection valve. The injected fuel forms a fog in the intake channel and is transported into a combustion chamber of the engine. The fuel is supplied to the injection valve by a fuel feed line which is essentially under constant pressure. If, for example, a high load is requested by the user, then the injection valve is so driven that it remains open relatively long. In this way, a larger quantity of fuel gets into the intake manifold.
The maximum possible injection duration of the injection valve is, however, limited. In intake manifold injections, the injection valve, in the extreme case, can be simply opened continuously. However, it is more advantageous to have a discrete opening operation because injection into an open inlet valve should not occur. For an open inlet valve, the injection valve should therefore be closed as much as possible. The state of a continuously open injection valve is also characterized as a “Dauerstrich”. The fuel is directly injected into the combustion chamber with gasoline-direct injection as likewise known from the marketplace. Here, the maximum possible injection duration equals the duration of the intake stroke plus the compression stroke as may be required.
If the user of the engine requests a high load, that is, for example, a high torque at a possibly high rpm, then it can happen that the requested injection duration of the injection valve is greater than the maximum possible injection duration. Since the maximum possible injection duration is, however, limited depending on the engine, a fuel quantity is injected corresponding to the maximum possible injection duration notwithstanding this higher requested injection duration. At the same time, a large air charge is supplied to the combustion chamber which corresponds to the requested high torque so that the mixture, which arrives in the combustion chamber, is overall too lean. This leads, on the one hand, to a non-optimal emission performance and, on the other hand, to an increased temperature of the engine and of the exhaust gas.
A sudden drop of the rpm and therefore a sudden slowing of the rpm increase can occur, when, for increasing rpm, the actual injection duration is limited by the maximum possible injection duration. This is realized, for example, in a motor vehicle as an acceleration jolt by the passengers or by the driver. In this way, the comfort with the use of the engine is limited.